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Kotlin – 26 – Lists in Kotlin

A list is a fundamental data structure in Kotlin used to store a collection of elements. Lists allow you to group and manage data efficiently, and they are part of the Kotlin Standard Library. In this article, we will explore lists in Kotlin, how to create them, manipulate their elements, and perform common operations.

Creating Lists

In Kotlin, you can create a list using the listOf() function. Here’s an example of how to create a list of integers:


val numbers: List<Int> = listOf(1, 2, 3, 4, 5)

This creates a read-only list of integers named numbers. You can also use the mutableListOf() function to create a mutable list that allows you to add, remove, or modify elements:


val mutableNumbers: MutableList<Int> = mutableListOf(1, 2, 3)
mutableNumbers.add(4) // Adds an element to the mutable list
Accessing List Elements

You can access elements in a list by their index. In Kotlin, list indices start at 0. Here’s how you can access elements from the numbers list:


val firstNumber = numbers[0] // Accessing the first element
val thirdNumber = numbers[2] // Accessing the third element

You can also use the get() method to access elements:


val secondNumber = numbers.get(1) // Accessing the second element
Iterating Over Lists

To iterate over the elements of a list, you can use various methods. One common approach is to use a for loop:


for (number in numbers) {
    println(number)
}

You can also use the forEach() function, which allows you to apply an action to each element in the list:


numbers.forEach { number -> println(number) }
Modifying Lists

Mutability depends on whether you have a read-only list or a mutable list. You can modify a mutable list by adding, removing, or updating elements. Here are some common operations:


val mutableList: MutableList<String> = mutableListOf("apple", "banana", "cherry")
mutableList.add("date") // Adding an element
mutableList.remove("banana") // Removing an element
mutableList[0] = "apricot" // Updating an element
List Operations

Kotlin provides various built-in functions to perform operations on lists. Some common operations include:

  • size: Returns the number of elements in the list.
  • isEmpty(): Checks if the list is empty.
  • contains(): Checks if the list contains a specific element.
  • indexOf(): Finds the index of the first occurrence of an element.
  • lastIndexOf(): Finds the index of the last occurrence of an element.
  • sorted(): Returns a new list with elements sorted in ascending order.
  • reversed(): Returns a new list with elements in reverse order.

Here’s an example demonstrating some of these operations:


val fruits: List<String> = listOf("apple", "banana", "cherry", "banana")
val size = fruits.size
val isEmpty = fruits.isEmpty()
val hasCherry = fruits.contains("cherry")
val bananaIndex = fruits.indexOf("banana")
val lastBananaIndex = fruits.lastIndexOf("banana")
val sortedFruits = fruits.sorted()
val reversedFruits = fruits.reversed()
Conclusion

Lists are essential data structures in Kotlin for organizing and managing collections of elements. Whether you need a read-only list or a mutable one, Kotlin provides convenient functions and operations for working with lists. Understanding how to create, access, iterate, and modify lists is fundamental to building Kotlin applications that handle data efficiently.